On Oct. 12, 1999, the world population reached six billion (Wright, 1999). At the turn of the twenty-first century the estimated population was 6.1 billion. With such a dramatic increase in population, it is obvious that there is an ever increasing need to feed the world's population.
Because only 11% of the world's soils are fertile enough to be farmed without serious limitation, intense pressure is placed on using less fertile soils. Drought is a major problem for approximately 28% of the land; mineral stress is a problem for an additional 23%. Most soils affected by drought are alkaline, whereas most affected by mineral stress are acidic (Foth and Ellis, 1997).
While fertility of deficient soils can be improved utilizing fertilizers containing appropriate amounts of essential elements for plant growth, these fertilizers may not contain the essential elements required by humans. This is especially true for crops grown upon acidic soils such as: lateritic, heavily-leached soils found throughout much of the tropical world (Moffat, 2000); silica-sand soils of Africa and Florida (Tan, 1998); young igneous soils containing larger fragments of unreactive feldspars and quartz, found in Zimbabwe and Zambia (Paton, 1978); and moderately acidic soils such as those in southeastern United States and many other parts of the world (Foth and Ellis, 1997). Thus, there is a need for fertilizers that contain essential elements required by both plants and humans to provide human populations with good physical and mental health.
Attempts to prepare such fertilizers have met with mixed results. Commercially available fertilizers are usually formulated by blending a mixture of various chemical compounds, which are not necessarily compatible. For example, the 12-12-12 microelements fertilizer, used on many illitic clay-loam soils, is one of the best commercial fertilizers on the market today. It consists of a granulated mixture of ammonium nitrate, urea, ammonium sulfate, and sulfuric acid blended with granular monocalcium/dicalcium phosphate (GTSP), granular potassium chloride, and granulated micro and trace elements. These are all essential nutrients needed to sustain healthy plant life (Foth and Ellis, 1997). After blending, fertilizer chemicals such as ureas can displace the hydrate water contained in the monocalcium/dicalcium phosphate compounds (Whittaker et al., 1933) yielding a sticky or soupy mess. Further, microelements such as iron can be readily oxidized to the plus three state (Fe3+) and react with phosphate anions (PO4−) to form an insoluble, unavailable ferric phosphate.
Even after application, many micro and trace element granules are so widely spaced that many plants cannot get all essential elements required for growth. Furthermore, bacterial action can result in 30% or more of the nitrogen value being lost to the atmosphere as nitrogen and nitrous oxide gases (Foth and Ellis, 1997). Finally, summer rains can wash soluble salts into aquifers, streams and lakes. Therefore, improvements need to be made to reduce the rate of release of nitrogen compounds and other essential elements to the soil.
In the late seventies, a slow-release fertilizer was developed by acidulating a high-assay phosphatic clay slime with sulfuric acid, then adding the micro and trace elements followed by formaldehyde, potassium chloride, and urea. This product worked well as a fertilizer, but was somewhat expensive and too slow in releasing essential elements.
In the late eighties, another slow-release fertilizer was developed for use in regions abundant in chicken populations. The initial mixture contained: ground chicken bones; viscera; ground phosphate ore; and sulfuric acid in which chopped chicken feathers had been dissolved. Micro and trace essential elements, potassium chloride, and urea or ammonium nitrate were added. This product was an adequate fertilizer, but limited in its application.
Thus there is a continuing need for improvements to slow-release fertilizers containing essential elements.
All references cited herein are incorporated by reference in their entirety, to the extent not inconsistent with the explicit teachings set forth herein.